The following United States Patents comprise the closest known prior art:
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In recent years the performance of disc-type magnetic data storage systems has been improved through improvements in two important areas: the increased density of data bits packed onto the disc surface, and reduced access time to drive the magnetic heads to a desired portion of the disc medium to read or write data thereon.
Generally speaking, the magnetic heads are driven linearly along the radius of the spinning disc to desired track locations on the disc. Although stepper motor arrangements are sufficient for low performance storage and retrieval systems, their inherent inertia, mechanical limitations, intrinsically limited positional resolution, and slow response time have prevented the use of these type of actuator drives in faster, high performance systems. To increase the linear speed of the head actuator assembly, disc drive designers have turned to voice coil drive systems which exhibit lower mass and higher driving force than the previous stepper motor arrangements. Such systems generally employ an electromagnetic voice coil slidably secured about the pole piece of a fixed magnet to generate the linear driving force. Indeed, such systems generally use a pair of driving coils spaced laterally on the carriage of the actuator assembly to provide balanced drive forces adjacent to the spaced apart side rails which support the carriage.
However, it has been found empirically that two coil drive systems or subject to vibration and resonance problems due to imbalances in the driving forces exerted by the paired coils. A slight change in the characteristics of one coil, due perhaps to heat, aging, or the like, can alter the magnetic output of that coil and the driving force generated thereby. When the forces of the two coils become unbalanced, the force couple resulting generates a torque which can disastrous effects on the actuator assembly. Thus, interest in electromagnetic drive systems has shifted to single coil arrangements which cannot suffer from such force imbalance problems.
In a single voice coil heat actuator device, it is desirable that the vector of the force generated by the coil be aligned through the center of gravity of the heat actuator assembly, so that no torque is applied to the assembly by the accelerating drive force of the coil. This vector alignment has generally been accomplished by the obvious approach of placing the mass comprised of the head arm assembly in linear alignment along the direction of the force vector of the coil. Thus, in the prior art devices the head arm assembly has extended from the carriage assembly along the axis of the voice coil. The net effect of this design approach is the creation of a carrige assembly which exhibits a relatively lengthy dimension along the axis of the coil. Due to the fact that the drive system is linear and aligned along the radius of the magnetic disc assembly, the overall length of the disc drive assembly of these prior art devices has been relatively large. This factor mitigates against the trend in the industry to design increasingly smaller disc drive systems with high performance and large storage capacity.
Another shortcoming in the prior art devices has been the E-frame magnetic drive structure itself. Generally speaking, in single coil carriage drive systems the end of the structure adjacent to the magnetic disc assembly has been open, so that the voice coil is permitted maximum translation along the core of the E-frame. However, in order to decrease the access time of the data storage system, it is necessary to increase the accelerating force by increasing the strength of the magnetic fields of the coil and the E-frame structure. Thus, higher driving forces applied to the carriage tend to require higher flux densities, and the presence of the open end of the E-frame adjacent to the magnetic discs poses the threat of increased data errors during the read/write operations.
It should also be noted that the voice coil type of carriage drive, unlike the stepper motor devices, provides no mechanical connection between the carriage and the base structure of the drive. Thus, when the coil is de-energized the carriage is relatively free to translate along the rails. During shipping and other movement of the system, the carriage can suffer damage through repeated impact against the mechanical stops generally employed at the limits of the carriage travel.